We observe a stable intermediate resistance switching state in the current perpendicular to plane geometry for all Co/Cu/Co double layer nanopillar junctions grown by molecular beam epitaxy. This novel state has a resistance between the resistances of the parallel and antiparallel alignment of both Co-layer magnetizations. The state, which originates from an additional in-plane magnetic easy axis, can be reached by spin transfer torque switching or by an external magnetic field. In addition to spin torque-induced coherent small-angle spin wave modes we observe a broad microwave emission spectrum. The latter is attributed to incoherent magnetic excitations that lead to a switching between the intermediate state and the parallel or antiparallel alignment of both ferromagnetic layers. We conclude that the additional magnetic easy axis suppresses a stable trajectory of coherent large-angle precession, which is not observed in our samples.
@article{arxiv.1201.2752,
title = {Intermediate state switching dynamics in magnetic double layer nanopillars grown by molecular beam epitaxy},
author = {N. Müsgens and T. Maassen and E. Maynicke and S. Rizwan Ali and A. Heiss and R. Ghadimi and J. Mayer and G. Güntherodt and B. Beschoten},
journal= {arXiv preprint arXiv:1201.2752},
year = {2012}
}